On the basis of the results from the foregoing characterizations, samples containing 10, 15, and 20 weight-percent of MWCNTs were scaled up to masses of ≈300 g and used to make specimens having dimensions of 10.2 by 15.2 by 0.32 cm. These specimens were molded by (1) injecting the mixtures, at temperatures between 260 and 280 °C, into a tool made of the low thermal-expansion alloy Invar® and then (2) curing for 1 hour at 371°C. The tool was designed to impart shear during the injection process in an attempt to achieve some alignment of the MWCNTs in the flow direction.

Qualitatively, the moldings from the 10 and 15 weight-percent samples appeared to be good. The moldings were subsequently characterized with respect to thermal, mechanical, and electrical properties. However, as expected from the results of the extrusion experiments, the 20 weight-percent sample could not be injected because of its higher viscosity.

The hardness value of each molded PETI-330/MWCNT specimen was found to be lower than that of the neat resin in the sense that an indenter was found to penetrate to a greater depth or an enhanced plastic deformation of the material was observed. The neat resin specimen was found to be electrically insulating. For the other specimens, the electrical resistivity was found to decrease with increasing concentration of MWCNTs, ranging from 8.86 × 10³ Ω /cm for the 10 weight-percent sample to 5.13 × 10³ Ω/cm for the 15 weight-percent sample. The thermal conductivities were found to increase with the proportion of MWCNTs, ranging from 0.219 W/(m·K) for the neat resin specimen to 0.577 W/(m·K) for the 10 weightpercent specimen and 0.777 W/(m·K) for the 15 weight-percent specimen. This trend in thermal conductivity suggests that nanotubes form networks in the polymer matrices that conduct heat, but not to the extent expected based on the high thermal conductivity of the MWCNTs.

This work was done by John W. Connell, Joseph G. Smith, Emilie J. Siochi, and Dennis C. Working of Langley Research Center; Jim M. Criss of M&P Technologies; Kent A. Watson and Donavon M. Delozier of the National Institute of Aerospace; and Sayata Ghose of the National Research Council. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Materials category. LAR-17082-1

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